The invention relates to a hydrogel string useful as a medical device and to a method for forming a hydrogel string. The method utilizes a device in which a prepolymer composition is brought into contact with a gelation initiator to form a hydrogel, which is then extruded from the device as the hydrogel string.
Hydrogels have been shown to be useful for a number of biomedical applications. For example, there are many instances in which an appropriate hydrogel biomaterial has been shown to be useful in repair of tissues and in augmentation of tissues, such as repair of defects and conditions in a tissue caused by disease, injury, or aging, repair of congenital defects and conditions in a tissue, and augmentation of tissues to provide a desirable functional, reconstructive, or cosmetic change. Bulking of the lower esophageal sphincter has been used for treatment of gastroesophageal reflux disease (GERD). Vesicoureteral reflux can be treated by endoscopic injection of a bulking agent in the submucosal space. Some types of incontinence can be treated by injection of a bulling agent into the submucosa of the urethra, in order to “beef up” the area and improve muscle tone. Spinal disc replacement or augmentation is another application where the use of hydrogels has been explored.
Another application for an appropriate hydrogel biomaterial is tissue embolization. Hydrogel embolic agents are useful for a variety of bioapplications, such as occluding blood vessels, occluding other body lumens such as fallopian tubes, filling aneurysm sacs, as arterial sealants, and as puncture sealants. Embolization of blood vessels is performed for a number of reasons, e.g. to reduce blood flow to and encourage atrophy of tumors, such as in the liver, to reduce blood flow and induce atrophy of uterine fibroids, for treatment of vascular malformations, such as arteriovenous malformations (AVMS) and arteriovenous fistulas (AVFs), to seal endoleaks into aneurysm sacs, to stop uncontrolled bleeding, or to slow bleeding prior to surgery.
Hydrogels have also been developed and used for drug delivery.
Hydrogel biomaterials can be preformed, such as hydrogel discs for drug delivery, or hydrogel microspheres for embolization. Hydrogels can also be formed in situ- at the site of embolization, for example. Each form has its advantages and disadvantages. Solid, preformed articles can be difficult to administer; larger articles can require invasive surgery and smaller articles can migrate after implantation. For example, solid particles and microspheres are generally unsuitable for filling aneurysms, particularly wide-necked aneurysms, due to migration of the particles or microspheres out of the sac.
Liquid, in situ formed materials can be flushed from the site during implantation. Another disadvantage is that the liquid may not form a cohesive solid mass, and bits of the hydrogel may be sloughed off over time.
Preformed polymeric strings have been proposed for use as biomaterials. U.S. Pat. No. 6,312,421 to Boock proposes preformed strings that are placed into a catheter for implantation. The strings are available in a set length, which reduces the flexibility of their use.
It would seem, therefore, that a hydrogel string that is formed at the time of delivery would be useful for many biomedical applications. The string would be available in the desired length, since it would be formed at the time of use.